Turbulent gas flux measurements below the air-water interface of a grid-stirred tank

Experiments have been conducted in an effort to elucidate the details of the interfacial gas transfer mechanism under liquid-side control. Near-surface liquid turbulence and oxygen concentration fluctuations have been measured in a laboratory grid-stirred tank for a range of turbulent Reynolds number R_L from 80 to 660. Our observations show that the thickness of the gas boundary layer closely agrees in trend and magnitude with the Lewis-Whitman's film thickness as determined from the bulk concentration change. Furthermore, the functional dependence on turbulent Reynolds number is consistent with a large eddy domination. Additional simultaneous measurements of turbulent velocity and oxygen concentration fluctuations, including direct flux measurements, give further indication that the large scale eddy motions are more effective in the interfacial mass transfer process.